Hypertrophic cardiomyopathy (HCM) is a prevalent cardiac disorder characterized by thickening of heart tissue due to excessive sarcomere replication. HCM contributes to a significant percentage of sudden unexpected cardiac death in any age group and is a cause of disabling cardiac symptoms. The force generating ??cardiac myosin heavy chain (?MHC) is one of the most common sarcomeric proteins mutated in HCM. How single mutations in the ?MHC result in HCM is unclear. The research proposed here will study different human ? MHC mutants on the single molecule level. The experiments will test: 1) changes at the single molecule level in ??cardiac myosin force production and 2) changes in the fraction of time the ??cardiac myosin spends bound to the filament out of the entire ATP cycle, the duty ratio. Even if the amount of force that an individual ??cardiac myosin mutant can exert does not differ from the wild type, a change in the motor's duty ratio influences the amount of total force that an ensemble of motors can produce (such as in the sarcomere). These experiments will involve a novel system to express and purify human??-cardiac myosin, optical trapping, motility assays and stop-flow kinetic assays. Understanding the effect of single point mutations on individual molecules is a necessary precursor to both understanding the role that ensembles of mutant motors play in hypertrophy and developing therapies that target the source of the disease. PUBLIC HEALTH RELEVANCE: Heart disease is an ever-present problem in the world, affecting all ages. Though we have made great progress in identifying symptoms and characteristics of heart disease, our current treatments and therapies are limited by a lack of information about the sources of the disease, on the level of the individual proteins that work together and make a heart function properly. I propose to directly study the influence of genetic mutations on these individual proteins that so that we can better develop treatments that target the source of heart disease.